Apple asserts that the iPad runs 10 hours on a charge of its nonremovable battery ... in my own test, the iPad played movies continuously ... [for] more than 12 hours. That’s four times as long as a typical laptop or portable DVD player.
This is one thing I've always found interesting. Apple underestimates their battery life in every product I've laid hands on, even under relatively high-power operations. And they claim longer battery life than any other similar product.